1. Field of the Invention
The present invention relates to a mat, a method of manufacturing a mat, and an exhaust gas purification apparatus.
2. Discussion of the Background
Conventionally, a nonwoven fabric-like mat obtained by compacting inorganic fibers such as silica fibers or alumina fibers has been known and this nonwoven fabric-like mat is excellent in properties such as heat resistance and elasticity (repulsive force), and therefore has been employed for various uses.
For example, a nonwoven fabric-like mat is used as a constituent material of an exhaust gas purification apparatus.
To explain specifically, a common exhaust gas purification apparatus is constituted by a column-like exhaust gas treatment body, a cylindrical casing for housing the exhaust gas treatment body, and a mat-like holding seal material disposed between the exhaust gas treatment body and the casing, and the nonwoven fabric-like mat is used as a material constituting the holding seal material.
The holding seal material is produced through a cutting step of cutting a nonwoven fabric-like mat into a prescribed shape.
Generally, of end surfaces of a holding seal material parallel to each other in the width direction, projected portions are formed in one end surface and recessed portions with a shape to be fitted with the projected portions when the holding seal material is wound on the column-like exhaust gas treatment body and the end surfaces are brought into contact with each other are formed in the other end surface (see FIGS. 1A and 1B).
When the holding seal material is disposed between the exhaust gas treatment body and the casing, the holding seal material is wound on the outer circumference of the exhaust gas treatment body in such a manner that the projected portions and the recessed portions are fitted with each other.
The holding seal material constituted by a nonwoven fabric-like mat having repulsive force has a prescribed holding force. Therefore, in the exhaust gas purification apparatus, the exhaust gas treatment body is firmly held in a prescribed position in the casing by the holding seal material. Further, since the holding seal material is disposed between the exhaust gas treatment body and the casing, the exhaust gas treatment body is hardly brought into contact with the casing even when vibration or the like is applied, and moreover, exhaust gas hardly leaks between the exhaust gas treatment body and the casing.
As a mat to be used as such a holding seal material, JP-A 9-946 discloses a binder mat produced by impregnating mat made from alumina fibers with an organic binder solution, subjecting the mat to a drying step, and carrying out hot air drying of the mat in a compacted state.
The produced binder mat is cut into a prescribed shape to produce a holding seal material.
Also, conventionally, a technique of carrying out needling treatment for a substrate mat made from inorganic fibers has been known. The needling treatment means pushing and pulling a fiber-interlacing means such as a needle or the like in and out the substrate mat. The inorganic fibers are interlaced three-dimensionally by carrying out the needling treatment, so that the shape of the mat can be maintained.
JP-A 62-56348, JP-A 2007-292040 and JP-A 2001-65337 disclose such needling treatment.
JP-A 62-56348 discloses execution of barb-needling treatment of pushing and pulling a barb needle having a plurality of barbs in and out in the thickness direction of a precursor sheet obtained by compacting alumina fiber precursors.
A mat disclosed in JP-A 2007-292040 is produced by adjusting the density range of an interlaced part formed by needling treatment. Accordingly, it aims to optimize both properties of strength and repulsive force.
JP-A 2001-65337 discloses a holding seal material in which interlaced parts formed by needling treatment are arranged in rows.
The contents of JP-A 9-946, JP-A 62-56348, JP-A 2007-292040 and JP-A 2001-65337 are incorporated herein by reference in their entirety.